1. Field of the Invention
The present invention generally relates to the manufacturing of semiconductor devices.
2. Discussion of the Related Art
In many semiconductor component manufacturing processes, silicon has to be deposited on a single-crystal silicon substrate, or on an area of this substrate. Several techniques are currently used.
A first, so-called epitaxial, type of deposition is performed under a reducing atmosphere and enables the crystal structure of the deposited layer to be in crystalline continuity with the substrate. These techniques require a deposition at high temperature, typically ranging between 1000.degree. C. and 1200.degree. C. for a deposition under atmospheric pressure and between 900.degree. C. and 1100.degree. C. under reduced pressure. The reducing atmosphere is obtained by using a mixture of reactive gases in hydrogen (H.sub.2).
Techniques, such as chemical vapor deposition (CVD), which enable silicon depositions at low temperature (500.degree. C. to 700.degree. C.) are also known. With these techniques, the deposited silicon is polycrystalline, or amorphous. More precisely, the size of the polysilicon grains decreases with temperature. At low pressure and at 550.degree. C., the deposited silicon is amorphous.
In many cases, at the end of the manufacturing process of an integrated circuit, silicon is desired to be deposited on a portion of a single-crystal silicon substrate to form either a substrate doping source, or a contacting area between an underlying layer and the external environment, or to simultaneously ensure both functions. It is then essential that the temperatures involved do not exceed a value on the order of 600.degree. C. to avoid undesirable dopant diffusions.